In larger electrical power systems, a typical drawout power circuit breaker is racked, i.e., connected or disconnected, from the energized electrical supply bus for maintenance or repair by a human operator. The human operator physically rotates a racking screw associated with the breaker in order to connect or disconnect the breaker to or from the electrical supply bus.
In order to effect the operation described above, the human operator stands within arms-reach of the circuit breaker, which also means he or she is in close proximity to the circuit breaker. If the circuit breaker should happen to fail catastrophically, the human operator is at risk of serious injury or death from the resulting arc-blast and flying debris.